Add --no-cache flag

source/types.ts

@@ -48,7 +48,7 @@ export declare interface Header {
   source: string;
   headers: {
     key: string;
-    value: string;
+    value: string | null;
   }[];
 }
 
@@ -78,6 +78,7 @@ export declare interface Options {
   '--no-request-logging': boolean;
   '--no-clipboard': boolean;
   '--no-compression': boolean;
+  '--no-cache': boolean;
   '--no-etag': boolean;
   '--symlinks': boolean;
   '--cors': boolean;

source/utilities/cli.ts

@@ -52,6 +52,8 @@ const helpText = chalkTemplate`
 
     -u, --no-compression                Do not compress files
 
+    --no-cache                          Disable browser caching
+
     --no-etag                           Send \`Last-Modified\` header instead of \`ETag\`
 
     -S, --symlinks                      Resolve symlinks instead of showing 404 errors
@@ -152,6 +154,7 @@ const options = {
   '--config': String,
   '--no-clipboard': Boolean,
   '--no-compression': Boolean,
+  '--no-cache': Boolean,
   '--no-etag': Boolean,
   '--symlinks': Boolean,
   '--cors': Boolean,

source/utilities/config.ts

@@ -12,7 +12,37 @@ import schema from '@zeit/schemas/deployment/config-static.js';
 import { resolve } from './promise.js';
 import { logger } from './logger.js';
 import type { ErrorObject } from 'ajv';
-import type { Configuration, Options, NodeError } from '../types.js';
+import type { Configuration, Header, Options, NodeError } from '../types.js';
+
+const noCacheHeader: Header = {
+  source: '**',
+  headers: [
+    {
+      key: 'Cache-Control',
+      value: 'no-store, no-cache, must-revalidate, proxy-revalidate',
+    },
+    {
+      key: 'Pragma',
+      value: 'no-cache',
+    },
+    {
+      key: 'Expires',
+      value: '0',
+    },
+    {
+      key: 'Surrogate-Control',
+      value: 'no-store',
+    },
+    {
+      key: 'ETag',
+      value: null,
+    },
+    {
+      key: 'Last-Modified',
+      value: null,
+    },
+  ],
+};
 
 /**
  * Parses and returns a configuration object from the designated locations.
@@ -137,8 +167,13 @@ export const loadConfiguration = async (
   }
 
   // Configure defaults based on the options the user has passed.
-  config.etag = !args['--no-etag'];
+  config.etag = !args['--no-etag'] && !args['--no-cache'];
   config.symlinks = args['--symlinks'] || config.symlinks;
 
+  if (args['--no-cache']) {
+    const headers = Array.isArray(config.headers) ? config.headers : [];
+    config.headers = [...headers, noCacheHeader];
+  }
+
   return config;
 };

source/utilities/server.ts

@@ -72,7 +72,9 @@ export const startServer = async (
         await compress(request as ExpressRequest, response as ExpressResponse);
 
       // Let the `serve-handler` module do the rest.
-      await handler(request, response, config);
+      // `serve-handler` supports `null` header values to remove default
+      // headers, but its published types only allow strings.
+      await handler(request, response, config as Parameters<typeof handler>[2]);
 
       // Before returning the response, log the status code and time taken.
       const responseTime = Date.now() - requestTime.getTime();

tests/__snapshots__/cli.test.ts.snap

@@ -41,6 +41,8 @@ exports[`utilities/cli > render help text 1`] = `
 
     -u, --no-compression                Do not compress files
 
+    --no-cache                          Disable browser caching
+
     --no-etag                           Send \`Last-Modified\` header instead of \`ETag\`
 
     -S, --symlinks                      Resolve symlinks instead of showing 404 errors

tests/config.test.ts

@@ -52,6 +52,48 @@ describe('utilities/config', () => {
     expect(configuration).toMatchSnapshot();
   });
 
+  // When `--no-cache` is passed, caching should be disabled for every path.
+  test('disable cache when requested', async () => {
+    const configuration = await loadConfig('non-existent', {
+      '--no-cache': true,
+    });
+
+    expect(configuration).toMatchObject({
+      etag: false,
+      headers: [
+        {
+          source: '**',
+          headers: [
+            {
+              key: 'Cache-Control',
+              value: 'no-store, no-cache, must-revalidate, proxy-revalidate',
+            },
+            {
+              key: 'Pragma',
+              value: 'no-cache',
+            },
+            {
+              key: 'Expires',
+              value: '0',
+            },
+            {
+              key: 'Surrogate-Control',
+              value: 'no-store',
+            },
+            {
+              key: 'ETag',
+              value: null,
+            },
+            {
+              key: 'Last-Modified',
+              value: null,
+            },
+          ],
+        },
+      ],
+    });
+  });
+
   // When the configuration source is deprecated, i.e., the configuration lives
   // in `now.json` or `package.json`, a warning should be printed.
   test('warn when configuration comes from a deprecated source', async () => {

tests/server.test.ts

@@ -97,4 +97,26 @@ describe('utilities/server', () => {
 
     expect(consoleSpy).not.toHaveBeenCalled();
   });
+
+  // Make sure cache-related headers can be disabled for served files.
+  test('disable cache headers', async () => {
+    const noCacheConfig = await loadConfiguration(process.cwd(), fixture, {
+      '--no-cache': true,
+    });
+    const address = await startServer({ port: 3005 }, noCacheConfig, {
+      '--no-cache': true,
+    });
+
+    const response = await fetch(address.local!);
+
+    expect(response.ok).toBe(true);
+    expect(response.headers['cache-control']).toBe(
+      'no-store, no-cache, must-revalidate, proxy-revalidate',
+    );
+    expect(response.headers.pragma).toBe('no-cache');
+    expect(response.headers.expires).toBe('0');
+    expect(response.headers['surrogate-control']).toBe('no-store');
+    expect(response.headers.etag).toBeUndefined();
+    expect(response.headers['last-modified']).toBeUndefined();
+  });
 });